Condensation and Evaporation of R134a, R1234ze(E) and R1234ze(Z) Flow in Horizontal Microfin Tubes at Higher Temperature

Hydrofluoro-olefin R1234ze(E) and the isomer R1234ze(Z) are anticipated to be environment-friendly alternatives of R134a. Especially, R1234ze(Z) is most likely to be suitable for high-temperature heat pumps in industries. The heat transfer characteristics of those refrigerants R134a, R1234ze(E) and R1234ze(Z) are experimentally compared in this study. Their heat transfer coefficient and pressure gradient in a horizontal microfin tube are measured at temperatures of 40 and 50 oC for condensation, and temperature of 30 oC for evaporation. The equivalent inner diameter, fin height, and surface enlargement to the equivalent smooth tube of the microfin tube are 5.34 mm, 0.255 mm, and 2.24, respectively. The thermodynamic and transport properties of R1234ze(Z) are calculated by Reprop (Lemmon et al., 2013) associated the fluid file provided by Akasaka (2013) that is proposed to fit the experimental data by Higashi et al. (2013) and Miyara et al. (2013). For condensation, the heat transfer coefficient and pressure gradient of R1234ze(Z) are higher than those of R1234ze(E) and R134a at mass flux of 200 kg m-2s-1 and heat flux of 10 kW m-2. This is mainly because of the higher vapor velocity due to lower vapor density, larger liquid thermal conductivity and latent heat comparing to R134a and R1234ze(E). The experimentally determined heat transfer coefficient and pressure gradient are reasonably agree with the predicted values by Cavallini et al. (2009), Yonemoto et al. (2006), and Kadzierski et al. (1998). For evaporation, at mass flux of 200 kg m-2s-1 and heat flux of 10 kW m-2, the heat transfer coefficient of R1234ze(Z) is somewhat higher than that of R134a and R1234ze(E) at only higher vapor qualities. The pressure gradient of R1234ze(Z) is notably higher than that of R134a and R1234ze(E). The experimental heat transfer coefficient and pressure gradient are agree well with predicted values by Chamra et al. (2007), Mori et al. (2002), Thome et al. (1997)